In the semiconductor industry that has achieved remarkable development in recent years, a thin film formation process using CVD, vacuum deposition, or the like constitutes an indispensable important part of a manufacturing process, and currently a large number of thin film formation apparatuses, etching apparatuses, and cleaning apparatuses operate. The greatest problems when these apparatuses are used are that large amounts of deposits and adhering materials form on places other than a substrate of interest, and etching occurs on objects other than the target substrate.
The removal of these deposits and adhered materials is generally performed by a wet method with a strong acid or a dry method with ClF3 or F2/N2.
For example, Patent Literature 1 discloses a technique of etching a silicon oxide film formed on the surface of an object to be treated, using an interhalogen gas (ClF, ClF3, ClF5, BrF, BrF5, IF, IF3, IF5, and IF7 as examples), a gas comprising a compound of oxygen and a halogen (OF2 gas as an example), and a compound comprising a hydrogen atom (H2O gas, alcohol gas, methane gas, and hydrogen gas as examples), and then etching the object to be treated, with either gas of the interhalogen gas and the compound comprising oxygen and a halogen. For ClF3, which is an interhalogen gas, the etching rate of a silicon oxide film is very slow, and therefore in the etching of an object to be treated having natural oxide film of silicon formed thereon, wet etching pretreatment using dilute hydrofluoric acid is necessary. Advantages of using a gas comprising hydrogen together with the interhalogen gas and cooling the object to be treated are that the object to be treated can be etched in a state close to a wet state and moreover the object to be treated on which the silicon natural oxide film is formed can be etched without pretreatment. On the other hand, it is necessary to cool the object to be treated, and debris released by the etching of the object to be treated may remain without gasifying.
In addition, Patent Literature 2 discloses a technique of using a halogen fluoride gas selected from ClF3, ClF, BrF, BrF3, IF, and IF3 and irradiating an object to be treated, with light (ultraviolet light or laser light) to anisotropically etch tungsten silicide or molybdenum silicide that is the object to be treated. An advantage is that the halogen fluoride gas is excited by ultraviolet light or laser light, and therefore it is not necessary to use plasma, and therefore etching that does not cause plasma damage to a semiconductor device can be performed, but a problem is that the light damages the object to be treated.
Further, Patent Literature 3 discloses a technique of using a mixed gas of a fluorine-based gas selected from ClF3, ClF, NF3, F2, and HF and a chlorine-based gas selected from Cl2 and HCl and irradiating a substrate with ultraviolet rays for excitation to continuously etch a silicon nitride film and a silicon film. The etching rate of the fluorine-based gas is higher in the order of silicon, silicon nitride, and silicon oxide, and on the other hand the chlorine-based gas is characterized by etching silicon but not etching silicon nitride or silicon oxide at all. An advantage is that by controlling the partial pressures of the fluorine-based gas and the chlorine-based gas, the silicon nitride film and the silicon film can be continuously etched without damaging the base. But, also in this method, damage to the object to be treated is caused by irradiation with ultraviolet rays.
On the other hand, Patent Literature 4 discloses a technique of etching only a silicon support substrate using ClF, ClF3, BrF, BrF3, IF, or IF3 as a halogen fluoride, to separate a semiconductor integrated circuit made on the silicon substrate, and also discloses a method in which in non-plasma etching using these gases, a silicon oxide film is not etched at all, and therefore only a silicon support substrate can be selectively etched, and a semiconductor integrated circuit can be separated without being damaged.
In addition, in a dry method, generally, an etching gas selected from various fluorine-based gases such as NF3, SF6, and CF4 is used from the viewpoint of the rapidity of the etching rate, the ease of operation, and the like. But, for etching using NF3, SF6, or the like, a plasma atmosphere is usually needed, and therefore the apparatus is greatly restricted, and another problem is that the gas itself (impurities contained in the gas, or by-products produced in processing and removal) is a new contamination source for a target substrate.